The launch of any spacecraft induces significant loads on the bus structure and all elements attached in addition to the forces that actually accelerate the payload into space. These include acoustic pressures, random vibrations, lateral and torsional forces, usually acting in combination and of sufficient magnitude to be significant design drivers for the spacecraft and any of its subcomponents. Spacecraft components whose function requires them to move or be repositioned after launch, such as, but not limited to, antenna arrays, pointing mechanisms, solar arrays, deployable masts, etc., must also be secured in their designed launch configuration in order to withstand the launch loads listed above and then be capable of successful release once in orbit so that they may fulfil their functions successfully.
The devices that secure these movable components during launch are generically referred to as Hold Down and Release Mechanisms (HDRMs). As part of their function to secure the move able components, they also usually form a significant part of the structural integrity of the secured component providing a connection to the spacecraft body of known rigidity and strength and allowing the secured component to be designed around those known capabilities. Having HDRMs capable of withstanding varying forces and torques allows the movable components to be more efficiently designed, thus lowering the overall mass of the spacecraft and providing a significant benefit to the spacecraft owner/operator.
HDRMs of various types have been used since the very first spacecraft flights and, because they form a significant part of the spacecraft structure, the connection between the moveable component and the rest of the spacecraft is usually under considerable load, generally in the form of significant tension, termed “pre-load” within the primary load sharing component within the HDRM. Affecting the release of the movable component from the spacecraft body involves eliminating this tension connecting the two. Virtually all existing HDRM devices release this connecting tension extremely quickly, in small fractions of a second, resulting in significant mechanical shocks to both the spacecraft and the released component. For extremely fragile or delicate spacecraft subsystems these shocks can be debilitating, requiring mitigation techniques to limit the damage these shocks can cause. Generally, these mitigation techniques involve making structures more robust which in turn results in added mass and reduced spacecraft performance and or increased launch costs.
In addition, the vast majority of existing HDRMs have a consumable element to the design with some part being broken, or burned through as part of the release process. This, then, requires that after each release cycle, including the needed testing release cycles required to prove the overall spacecraft design prior to launch, that some part of the HDRM must be replaced. Further reducing confidence in the release that occurs after launch, is the fact that the part that is actually the most important has never actually been tested. It is impossible with these systems to actually test every portion of the mechanism that is launched prior to flight. At least one sub component of the HDRM is new and untested at the time of first (and often only) release in space.
Presently, there are no HDRM mechanisms which release secured movable spacecraft components, provide the structural connection between the spacecraft and the released component, release the component with near-zero shock and are fully resettable with no new consumable sub components required.